Q: If a DNA sequence is 5'-ATGCCGTA-3', what is the complementary DNA strand?

$$5'\text{-}TACGGCAT\text{-}3'$$

Question 1

Which of the following best describes the structure and location of the bacterial chromosome?

Accepted Answer

It is a single, circular DNA molecule found in the nucleoid region of the cell.

Question 2

A scientist discovers a bacterial cell that can transfer antibiotic resistance genes to another cell through direct contact. Which type of horizontal gene transfer is this, and what structure is primarily involved?

Accepted Answer

Conjugation; pilus

Question 3

During DNA replication, which enzyme is responsible for joining Okazaki fragments on the lagging strand?

Accepted Answer

DNA ligase

Question 4

If a DNA sequence is 5'-ATGCCGTA-3', what is the complementary DNA strand?

Accepted Answer

$$5'	ext{-}TACGGCAT	ext{-}3'$$

Question 5

Which of the following statements about the lac operon is correct?

Accepted Answer

It is induced in the presence of lactose and absence of glucose.

Question 6

A point mutation that changes a codon from UAU (tyrosine) to UAA (stop codon) is best described as:

Accepted Answer

Nonsense mutation

Question 7

Which of the following best explains why broad-spectrum antibiotics can lead to secondary infections such as Clostridioides difficile colitis?

Accepted Answer

They disrupt normal microbiota, reducing microbial antagonism.

Question 8

Which of the following is NOT a mechanism by which bacteria can develop resistance to antimicrobial drugs?

Accepted Answer

Increasing the rate of DNA replication

Question 9

Which of the following statements about prions is TRUE?

Accepted Answer

They are infectious proteins that cause neurodegenerative diseases.

Question 10

A hospital is considering using ethylene oxide to sterilize surgical instruments. Which of the following is a disadvantage of this method?

Accepted Answer

It is toxic and requires lengthy aeration to remove residues.

Question 11

Which of the following best describes the difference between an inducible and a repressible operon?

Accepted Answer

Inducible operons are usually off and can be turned on; repressible operons are usually on and can be turned off.

Question 12

Which of the following is a function of tRNA during translation?

Accepted Answer

It carries amino acids to the ribosome and matches them to the mRNA codon via its anticodon.

Question 13

Which of the following best describes the action of beta-lactam antibiotics?

Accepted Answer

They inhibit cell wall synthesis by preventing cross-linking of peptidoglycan.

Question 14

A patient is prescribed a drug that inhibits bacterial translation but does not affect eukaryotic cells. What is the most likely explanation for this selective toxicity?

Accepted Answer

Bacterial ribosomes are 70S, while eukaryotic ribosomes are 80S.

Question 15

Which of the following statements about viral genomes is correct?

Accepted Answer

They can be composed of either DNA or RNA, and may be single- or double-stranded.

Question 16

Which of the following best describes the process of lyophilization?

Accepted Answer

It preserves microbes by freezing and drying them under vacuum.

Question 17

A laboratory is using UV light to control microbial growth on surfaces. Which statement best describes the mode of action of UV light?

Accepted Answer

It causes the formation of thymine dimers in DNA, leading to mutations.

Question 18

Which of the following is a key difference between the lytic and lysogenic cycles of bacteriophage replication?

Accepted Answer

In the lysogenic cycle, the viral genome integrates into the host genome and can remain dormant.

Question 19

Which of the following best describes the function of an F plasmid in bacterial conjugation?

Accepted Answer

It carries genes required for the formation of the sex pilus and DNA transfer.

Question 20

A patient is infected with a virus that has a single-stranded, negative-sense RNA genome. Which of the following must occur before viral proteins can be synthesized?

Accepted Answer

The viral RNA must be transcribed into complementary positive-sense mRNA.

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